(1) Field of the Invention
The present invention relates to an interface circuit that can switch between a voltage driving push-pull type single-ended transmission system and a current driving type differential transmission system in an interface between machines and an interface between LSI's.
(2) Description of the Related Art
In recent years, processing speed of electronic devices has been continued to be improved in order to satisfy demands for multifunctional and high functional electronic devices. With the improvement, communication speed between the electronic devices has been enhanced. With the use of single-ended transmission having been conventionally and commonly used, it is difficult to realize high-speed communication between the electronic devices. Accordingly, in various types of transmission standard by which high-speed signal transmission is performed, such as LVDS (Low Voltage Differential transmission), USB (Universal Serial Bus) 2.0, IEEE 1394, HDMI (High-Definition Multimedia Interface) and Serial-ATA, a current driving type differential transmission system is employed in an interface of the electronic device.
In the field of a removable memory card, of which an SD memory card is a representative, currently the voltage driving type single-ended transmission system is employed as an interface with a host machine. However, it is necessary to apply the current driving type differential transmission system that enables high-speed input and output of data to a removable memory card whose storage capacity is increased with the development of technology.
However, if the current driving type differential transmission system is applied to a removable memory card, this removable memory card cannot be used in an electronic device that employs the already-available voltage driving type single-ended transmission system.
Therefore, there has been a demand for a removable memory card that can use both of the current driving type differential transmission system and the voltage driving type single-ended transmission system for data transmission. However, since the shape, the number of signals and terminals of a memory card are defined, besides the signal lines used for the already-available voltage driving type single-ended transmission system, the memory card cannot be provided with additional signal lines used for the current driving type differential transmission. Accordingly, signal lines and terminals of the memory card need to be shared for the use of both of the voltage driving type single-ended transmission system and the current driving type differential transmission type.
To solve the above problems, Patent Document 1 discloses a circuit that selectively uses the voltage driving type single-ended transmission and the current driving type differential transmission with the use of common signal lines. According to this technique disclosed by Patent Document 1, two output terminals of a single-ended driver are connected to two signal lines, respectively. Furthermore, the two signal lines are respectively connected to two output terminals of a differential driver. In addition, according to a transmission system control signal, the circuit switches between the single-ended driver and the differential driver for the operation. Herein, the transmission system control signal is a control signal indicating either of the single-ended transmission and the differential transmission.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2000-353035